MEF-330-2K-Plus, 80-10 EFHW matching coil for high bands

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7F, May 31, 2021.

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  1. WA7F

    WA7F Premium Subscriber QRZ Page

    There really aren’t space issues here. A 160 meter end feed would fit the west to east run but, the pattern on 20m would be a mess.

    I’m running out of time, must go on a trip and need to use this antenna remotely. I’ll install a new wire or flip the existing wire around this afternoon so the coil located six feet from the transformer. This will be compromise for 75m, at least for the time being. It will be a couple of weeks before I can try anything else but, I’m still interested in other solutions. Perhaps adding a cap at the mid point is the way to go. Anyway, there is time to think about it.
     
    Last edited: Jun 1, 2021
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    David,

    I cobbled a sim of your description, and what you have cannot work as a multiband EFHW fed through a 1:49 transformer... The problem is the connection/proximity to the tower. This is exactly what I wrote about in the 160m EFHW fed off the old ATT Tower thread, where I went to great pains to completely isolate (using the in-line stretched-out coax and common-mode choke) so as to isolate, to the greatest extend possible, the EFHW from the grounded tower structure.

    Your antenna is basically a down-sloping wire fed against a grounded tower, what is known as a "sloper". This makes the antenna into a grounded Marconi where most of the radiation is from the tower itself, and the wire(s) hanging off to the side are just a means ("counterpoise") that inject current into the tower (not very effectively, either).

    The "sloper" idea could be refined into useful mono-band antennas (160m, 80m, 75m or 40m). These would not have the 2X,3X,4X,... resonances of an EFHW, however, nor would they use a 1:49 transformer, because their native feedpoint impedance would be low (30 to 100 Ohms).
     
    Last edited: Jun 1, 2021
  3. G0KDT

    G0KDT Ham Member QRZ Page

    Well, the original thread on the 160 wire reported problems and went through many options to resolve it... the way the thread ended implied that it was working along side a 5rv that could also be used. That said, it and on reflection it didn't really go into how well the final install worked.

    So that kind of bins the information presented or should say it doesn't work... ?
     
  4. WA7F

    WA7F Premium Subscriber QRZ Page

    Hi Mike,
    Thanks for looking at the problem. I think I’ll give it one more try anyway and if it fails I’ll hang a quick dipole for 20m and bring the LDF4 online ahead of schedule. It’s just going to be a long day getting everything done.

    The XYL is whining about all the wires and a transformer hanging in the air would probably result in a battle. Plus, I wouldn’t want to look at it hanging there either. So I’m not knocking your technique, it just isn’t practical for my situation.

    FYI - The 160m EFHW is working great with the transformer mounted on the tower and grounded to the tower. Not to say that something else wouldn’t work better. One of these days I’ll disconnect the ground to see if there is any difference.

    Dave -
     
  5. WA7F

    WA7F Premium Subscriber QRZ Page

    So I moved the coil to about six feet from the the 49:1 transformer and left the total length at 130’. Actually, the coil is seven feet from the transformer if you count the loop from the insulator to the transformer. I’d post the SWR plot but it’s on another PC and it’s late. As expected, the best 80m meter SWR is around 3.476 and the 20m dip is a bit high at 14.390 or so. It’s less than ideal but the K3 will tune 80m to about 3.790 MHz to 2:1 and all of 20m. It good enough to get started on the remote K3 mini. I’ll pick up the tuning again in a couple of weeks.

    At some point this month, I’ll try the the 300pF capacitor that WA7ARK suggested on page 28 of his PowerPoint at improve 80m.
     

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